Abstract
Non-cytopathic strains of bovine viral diarrhoea virus (BVDV) readily establish persistent infections in cells of bovine origin. The involvement of endogenous interferon (IFN) on the maintenance of the infection level, as well as the effect of exogenous IFN and tumour necrosis factor alpha (TNF-α), was studied. Although exogenous IFN suppressed the spread and replication of virus, it did not cure the infection, even when continuously present over many cell passages. TNF-α alone had no antiviral effect in this system. However, both TNF-α and IFN enhanced the cytopathic effect of cytopathic BVDV, and induced a BVDV-like cytopathic effect in cells infected with non-cytopathic BVDV. These data are discussed with regard to possible mechanisms of pathogenesis during fatal BVDV disease in cattle.